Huang, Yiqin, and Jiang Zhu. “A Personalized English Learning Material Recommendation System Based on Knowledge Graph”. International Journal of Emerging Technologies in Learning (iJET) 16, no. 11 (June 4, 2021): pp. 160–173. Accessed August 8, 2022. https://online-journals.org/index.php/i-jet/article/view/23317.